In a skillet, fry corn tortillas in vegetable oil over medium heat until crispy (about 1 minute per side).
Drain tortillas on paper towels.
Add diced chicken to skillet and sprinkle with taco seasoning. Sauté for a few minutes, then move to a serving bowl.
Add black beans to skillet and mash until most beans are broken. Add salsa and a little bit of the cilantro. Sauté over medium heat until beans are thickened and creamy, about 5 minutes.
To assemble tostadas, start with the fried tortillas. Spread black bean mixture on tortillas, then add chicken. Top with tomatoes, lettuce, cilantro and crumbled queso fresco.
Drizzle with sour cream if desired, or other toppings of your choice.
Notes
Use corn tortillas that are a few days old for best results. If tortillas are moist, dry them on a sheet pan in a 275 degree oven for 5 minutes before frying.
If you can't find queso fresco at the grocery store, feel free to substitute cojita or feta cheese instead.
Turn your tortillas into a fiesta by creating a Tostada Bar! Set out fried tortillas with bowls of toppings and encourage guests to build their own tostadas.